During the operation of an industrial plant in which gases are generated or processed, the parameters of which, for example composition, temperature etc., it is necessary to monitor, corresponding gas sensors are used. Often, however, such gas sensors cannot be positioned directly at the measurement site since conditions unsuitable for the sensor, for example excessively high temperatures, prevail there. In order nevertheless to be able to determine the gas parameters, it is necessary to place the sensors at a suitable distance from the measurement site. The gas to be analyzed must in this case be fed from the measurement site to the gas sensor by means of a suitable feed line.
For example, in DE 10 2012 217 596, in order to measure corrosive conditions in a boiler of a thermal power station, sensor devices are used which comprise a gas feed through the boiler wall with an opening toward the interior of the boiler and a sensor chamber outside the boiler. A sensor element for detecting the stoichiometry of a combustion taking place in the boiler is arranged in the sensor chamber, in order to monitor the combustion inter alia so as to improve the energy efficiency and to limit the emissions. The sensor in the sensor chamber is accordingly arranged separated from the actual measurement site.
If the gas to be measured then lies in a region with a reduced pressure, or generally with varying pressure conditions, in order to ensure continuous and reliable monitoring the gas needs to be actively delivered from the measurement site to the sensor element. To this end, separate pumps are generally used, which extract a part of the gas from the measurement site and deliver it to the sensor element in the sensor chamber. However, such an external pump constitutes additional outlay for the overall system, and besides the corresponding additional costs the restricted operational reliability and the finite lifetime of the pump also have detrimental effects.
In order to overcome these disadvantages due to the use of the pump, the system may for example be operated without a pump, the gas diffusion which takes place anyway being used as a transport mechanism for the gas from the measurement site to the sensor element. A disadvantage which occurs in this case is that even small pressure differences between the gas feed and the gas discharge can cause the diffusive gas flow to be stopped or to be superimposed with an undesired flow.